I think the elephant comes from semantics. There is Cuckolding, wife is going out on husband who gets nothing. And there is Wife Sharing, where the wife gets what she wants, and the husband does to. May be together, may be apart.
In our house and for me, it's all about my wife and what she wants. When we got married, she was a virgin, for over 15 years she had never had anyone or anything other than my cock. To spice things up we got her a few toys. That lead to her choosing some toys, and her wanting to try some dildos of different sizes and colors. That lead to a long conversation one weekend where I told her I was ok if she wanted to try another real cock. About 6 months later she was visiting an old college friend and they all ended up naked in the hot tub. It has gone from there.
Some guys like the idea of being humiliated, locked in chastity, and such. To me that is just being submissive. Some guys just can't handle the idea of sharing their wife because they are intimidated. I think for a true open marriage you have to have satisfaction on both sides. As long as you're both getting what you want, what is the big deal. Your adults, it's your relationship, who cares what others think or say. I mean my wife has a younger sister who doesn't even have sex for fun. The only time she is naked with her husband is to try and get pregnant. That is what I can't understand.